Exodus 12 : 37-42
The Israelites left Rameses for Succoth, about six hundred thousand of them on the march, counting the men only, and not the children. A great number of other people of all descriptions went with them, as well as sheep and cattle in droves.
With the dough they had brought with them from Egypt, they made cakes of unleavened bread. It had not risen, for when they were driven from Egypt they could not delay and had not even provided themselves with food.
The Israelites had been in Egypt for four hundred and thirty years. It was at the end of these four hundred and thirty years to the very day that the armies of YHVH left Egypt. This is the watch for YHVH who brought Israel out of Egypt. This night is for YHVH, and all the Israelites are also to keep vigil on this night, year after year, for all time.